1. Field of the Invention
The present invention relates to machinery for processing foods. In particular, the invention relates to a machine for processing dough into relatively thin sheets out of which are cut chips, tortillas, and like food products.
2. Description of Related Art
Tortillas are the indigenous "bread" of the New World civilizations. The major grain of the Americas was maize (corn). Since corn kernels lack the elastic gluten proteins of wheat, native Americans were not able to produce a leavened bread instead, they developed a technique in which dried maize is cooked with calcium carbonate or alkali to produce a sticky dough known as masa. Traditionally this dough was shaped by hand and baked on a stone comal or griddle. Today, special machines called sheeting heads form the masa into relatively thin sheets from which tortillas and other food products such as chips are cut.
The typical sheeting head comprises a hopper structure which contains the masa. The hopper comprises two endwalls and may also include two sidewalls. Masa dough is held in the space included by the hopper walls. At the bottom of the hopper is a pair of counterrotating parallel rollers which may also act as the hopper sidewalls. The rollers rotate on a horizontal axis drawing in the masa and forming it into a sheet. After the masa is squeezed between the two rollers, it is stripped off one of the rollers and transferred to the other roller, usually by a stripper wire. On the second roller the sheet of dough interacts with a rotary cutter which rotates in contact with that roller thereby cutting the dough into the desired shapes. The cut dough is then stripped from the sheeting roller and transferred to a conveyor belt, which carries it into an oven or other processing station.
The sheeting head is susceptible to a great many variations and improvements. The basic form of the device is, to some degree, dictated by the sticky, plastic masa dough. Because the dough is sticky, it must be physically stripped from the roller. Because the dough is plastic, it tends to expand outward as it's squeezed between the rollers. Thus, it has a tendency to escape from the hopper along the junction of the hopper endwalls with the rollers. This can be a considerable problem, as the dough can penetrate into the bearings and other machine parts. A prior art solution is to add an additional component to the endwalls of the hopper. An insert, which is contoured to match the upper surfaces of the rollers, is attached to the inner surface of the endwall and because of its shape, blocks escape of dough between the inner surface of the endwall and the end surfaces of the rollers.
Nevertheless, the plastic dough still is able to work its way under the contoured edges of the insert and wedge itself between the ends of the rollers and the endwall. As already mentioned, the insert is shaped to tightly contact the upper surfaces of the two rollers. Therefore, the insert comes to a narrow point-shaped tip which is inserted between the rollers. A buildup of dough could actually force the endwall to bend, thereby opening a gap and allowing even more dough to escape. The narrow tip of the insert is especially prone to deformation. To avoid such lateral motion of the endwalls, various mechanisms have been employed to exert an inward pressure on the endwalls.
One prior art method that attempts to minimize the escape of dough under the contoured edges of the insert can be seen in U.S. Pat. No. 5,180,593 to Mistretta et al. FIG. 9 of that patent shows the insert, there called a saddle, constructed with a lip which is intended to ride along a shoulder that has been cut into the end of the roller. The intent of this structure is to reduce the escape of the dough under the lip; however, the lip cannot prevent distortion of the insert caused by build up of dough and frictional heating.